In the firing of industrial oil burners and auxiliary or igniter burners associated with large oil fired utility or industrial boilers, it is a conventional practice to employ steam as an atomizing agent for the fuel oil. Moreover, the same source of steam is usually employed in purging fuel oil lines for safety and other considerations. A combination valve of the type under consideration and which control the supply of both steam and fuel oil during firing and purging operations of burner systems is shown in U.S. Pat. No. 4,146,056 issued Mar. 27, 1979 and entitled STEAM AND FUEL OIL CONTROL AND PURGE VALVE. The valve shown and described in the patent, which is incorporated herein by reference, is particularly well suited to the efficient control of firing and purge operations as aforesaid and is quite satisfactory in all respects. There is, however, one additional feature recently found desirable and which is lacking in the patented valve.
More particularly, oil supplied to the type of burners mentioned may be highly viscous and it may be necessary to heat the same in its storage tank in order to lower its viscosity and thereby provide for the free flow of the oil to the burner. When the fuel oil valve is closed and oil flow terminated, the oil may become highly viscous and create an impediment or even preclude restarting of the burner. If, on the other hand, oil is recirculated to the tank for reheating when its control or supply valve is closed, a desirably low level of oil viscosity may be maintained in the line leading to the valve and returning therefrom to the tank.
It is a general object of the present invention to provide an improved combination steam and fuel oil supply valve of the type mentioned and which includes a simple and straight-forward means providing for the recirculation of fuel oil from the valve to its storage tank or reservoir when the valve is closed to terminate the flow of fuel oil to its associated burner.